My patients sometimes look at me funny when I tell them to wear sunscreen in the winter. Maybe it's because I live in Canada, where winters are long and harsh, and are characterized by none of the sunny weather that one might associate with sunburns and skin cancer risk. And yet, dermatologists in northern climates usually recommend daily sun protection, even in the winters. What are the reasons for this?

The answer lies with the nature of the radiation, known as ultraviolet radiation (UVR), that reaches the earth from the sun, and causes skin cancer, skin aging, and eye diseases such as cataracts. This radiation is divided into two groups: ultraviolet B (UVB) and ultraviolet A (UVA). In general, UVB rays are more energetic, and they bear more responsibility for sunburn and skin cancer. Longer UVA rays are also carcinogenic (cancer-causing), and they are the primary cause of skin aging.

While UVB rays are significantly less intense in the winters in cold climates, UVA rays fluctuate less with the season. So while we are far less likely to burn in the winters, we are still exposed to vast amounts of ultraviolet A radiation.

I know, you're thinking that you're barely even outside in the depths of winter, as you shuffle from your house to your car, and then to work. You might consider, however, that UVA rays also penetrate window glass, and so, again, you are still exposed to considerable radiation even while sitting in front of your window at work or while driving in your car. The photo below demonstrates the dramatic effect that sunlight, even through windowpane, has on the skin. It was taken of a truck driver who spent his career with one side of his face exposed to his car window. His skin has aged more quickly on the side of his face that received decades of UVA radiation, including through his car's window.

It has been estimated that 90% of skin aging is caused by exposure to sunlight, and there is no question that the most powerful strategy you can use to prevent skin aging is to use a "broad spectrum" sunscreen daily, even in the winters. While I recommend using one with a minimum SPF of 30 in the summers, in Canada an SPF of 15 is sufficient in the winters (if you live in a warm climate, opt for an SPF of 30). It is important, all year, to choose one that provides protection from UVA rays. In order to do so, look for a product that bears the term "broad-spectrum" on the label, and contains the ingredients zinc oxide, bisoctrizole, avobenzone or ecamsule.

It has never been easier to choose a sunscreen than it is today. A plethora of options exist, and sunscreens can be found as lotions, gels, creams, sprays, sticks and powders. Because skin dryness is often a problem during our Canadian winters, moisturizers that contain added sunscreen ingredients are often a good choice this time of year. Examples of such products that provide good protection from UVA rays include Aveeno Positively Radiant Daily Moisturizer SPF 30 and Olay Complete All Day UV Moisturizer SPF 15. Alternatively, continue using your summer sunscreen - many of these have added moisturizing ingredients, or can be layered with your favourite moisturizer.

Dr. Michelle Levy is a board-certified dermatologist specializing in medical and aesthetic dermatology. A graduate of the University of Toronto's Faculty of Medicine, Dr. Levy provides a full spectrum of dermatologic services in Toronto, Canada.
Education:
M.D., University of Toronto, 1999
Residency in Dermatology, University of Toronto, 1999-2004
Employment History:
Self-employed, North York, Ontario, 2005-Present
Medcan. Consultant Dermatologist. 2007-Present